Magnetic field source detecting apparatus and magnetic field source detecting method

ABSTRACT

In a magnetic field source detecting apparatus, a magnetic sensor unit detects an intensity and a direction of a measurement target magnetic field on or over a surface of a test target object; and a position estimating unit estimates a position in a depth direction of a magnetic field source that exists at an unspecified position inside a test target object on the basis of the intensities and the directions of the measurement target magnetic field detected by the magnetic sensor at at least two 2-dimensional positions of the surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application relates to and claims priority rights from JapanesePatent Application No. 2018-202362, filed on Oct. 26, 2018, the entiredisclosure of which is hereby incorporated by reference herein.

BACKGROUND Technical Field

The present invention relates to a magnetic field source detectingapparatus and a magnetic field source detecting method.

Background Art

In a magnetic field source estimating method, an inner part of a testobject is expressed as a 3-dimensional cubic lattice net, and usingdetection coils and a SQUID (superconducting quantum interferencedevice) arranged in the outside of the test object, an electric currentdistribution at nodes in the 3-dimensional cubic lattice net isestimated as an electric current distribution in the test object (seePATENT LITERATURE #1).

Meanwhile, in an electric conductivity distribution deriving method, amagnetic sensor (TMR sensor) is scanned for obtaining magnetic fieldinformation over a surface of a test target object and thereby themagnetic field information is obtained, and a 2-dimensional internalelectric conductivity distribution in the test target object (i.e.2-dimensional electric conductivity distribution corresponding to thescanning plane) is derived (see PATENT LITERATURE #2).

CITATION LIST Patent Literature

PATENT LITERATURE #1: Japanese Patent Application Publication No.H5-220123.

SUMMARY Technical Problem

Although the aforementioned magnetic field source estimating method iscapable of estimating the internal current distribution using the SQUIDfrom an external magnetic field intensity distribution measured by thedetection coils, the SQUID requires a very high cost and therefore isnot practical in a general industry field (in particular, manufacturingindustry field).

Further, although the aforementioned electrical conductivitydistribution deriving method is capable of deriving the 2-dimensionalelectrical conductivity distribution, it hardly detects an electricalconductivity variation in a depth direction of the test target object.

The present invention is conceived in view of the aforementioned problemand aims for providing a magnetic field source detecting apparatus and amagnetic field source detecting method capable of estimating a positionof a magnetic field source in a depth direction inside a test targetobject at a relatively low cost.

Solution to Problem

A magnetic field source detecting apparatus according to an aspect ofthe present invention includes a magnetic sensor unit that detects anintensity and a direction of a measurement target magnetic field on orover a surface of a test target object; and a position estimating unitthat estimates a position in a depth direction of a magnetic fieldsource that exists at an unspecified position inside a test targetobject on the basis of the intensities and the directions of themeasurement target magnetic field detected by the magnetic sensor at atleast two 2-dimensional positions of the surface.

A magnetic field source detecting method according to an aspect of thepresent invention includes the steps of: (a) detecting intensities anddirections of a measurement target magnetic field at at least two2-dimensional positions of a surface of a test target object using amagnetic sensor unit that detects an intensity and a direction of themeasurement target magnetic field on or over the surface of the testtarget object; and (b) estimating a position in a depth direction of amagnetic field source that exists at an unspecified position inside thetest target object on the basis of the intensities and the directions ofthe measurement target magnetic field detected at the at least two2-dimensional positions.

Advantageous Effects of Invention

By means of the present invention, provided are a magnetic field sourcedetecting apparatus and a magnetic field source detecting method capableof estimating a position of a magnetic field source in a depth directioninside a test target object at a relatively low cost.

These and other objects, features and advantages of the presentdisclosure will become more apparent upon reading of the followingdetailed description along with the accompanied drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram that indicates a configuration of a magneticfield source detecting apparatus in an embodiment of the presentinvention;

FIG. 2 shows a perspective view of a current as a magnetic field sourceinside a test target object;

FIG. 3 shows a perspective view that explains scanning of a magneticsensor 10 in Embodiment 1;

FIG. 4 shows a diagram that explains a magnetic field induced by acurrent as a magnetic field source;

FIGS. 5A and 5B show diagrams that explain estimation of a position in adepth direction of a current as a magnetic field source in Embodiment 1;

FIG. 6 shows a diagram that explains plural orientations of an NVcenter;

FIG. 7 shows a diagram that explains a frequency characteristic offluorescence intensities corresponding to plural orientations of an NVcenter after Zeeman splitting of the NV center;

FIG. 8 shows a diagram that indicates an example of a leakage current asa magnetic field source that occurs between electrodes inside a testtarget object;

FIG. 9 shows a diagram that indicates another example of a leakagecurrent as a magnetic field source that occurs between electrodes insidea test target object; and

FIG. 10 shows a diagram that indicates formulas in an example ofmagnetic field analysis.

DETAILED DESCRIPTION

Hereinafter, embodiments according to aspects of the present inventionwill be explained with reference to drawings.

Embodiment 1

FIG. 1 shows a diagram that indicates a configuration of a magneticfield source detecting apparatus in an embodiment of the presentinvention. FIG. 2 shows a perspective view of a current as a magneticfield source inside a test target object. The magnetic field sourcedetecting apparatus shown in FIG. 1 detects a current I as a magneticfield source inside a test target object 100 as shown in FIG. 2. InEmbodiment 1, the magnetic field source is (a) a current (e.g. a leakagecurrent between electrodes or the like) that flows at an unspecifiedposition inside the test target object 100 or (b) a current that flowsat one of conduction paths laid in multilayers (e.g. wiring patternslaid on a front surface and a back surface of a single layer circuitboard, wiring patterns laid on layers of multilayer circuit board or thelike). Further, the test target object 100 is composed of a nonmagneticmaterial.

The magnetic field source detecting apparatus shown in FIG. 1 includes amagnetic sensor unit 10, a processor 11, and a high frequency powersupply 12.

The magnetic sensor unit 10 detects an intensity and a direction of ameasurement target magnetic field on or over the test target object 100.At each of measurement positions, the magnetic sensor unit 10 detectsthe intensity and the direction of the measurement target magnetic fieldat the same time.

In this embodiment, the magnetic sensor unit 10 includes an opticallydetected magnetic resonance (ODMR) member 1, a coil 2, a referencemagnetic field generating unit 3, an irradiating device 4, and a lightreceiving device 5.

In this embodiment, the ODMR member 1 includes plural specific colorcenters. Each of the plural specific color centers has aZeeman-splittable energy level and can take plural orientations of whichenergy level shift amounts due to Zeeman splitting are different fromeach other.

Here the ODMR member 1 is a board member such as a diamond includingplural NV (Nitrogen Vacancy) centers as the specific color centers of asingle type, and is fixed to a support board 1 a. In the NV center, theground level is a triplet level of Ms=0, +1, −1, and levels of Ms=+1 andMs=−1 are Zeeman-splittable. Further, as mentioned below, in accordancewith a positional relation between an atom (here, nitrogen) and avacancy in a diamond crystal lattice, an NV center can take fourorientations of which energy level shift amounts due to Zeeman splittingare different from each other.

The coil 2 applies a magnetic field of a microwave to the ODMR member 1.A frequency of the microwave is set in accordance with a type of theODMR member 1 (i.e. in accordance with an energy difference betweensublevels of a ground level of the specific color center). For example,if the ODMR member 1 is a diamond including an NV center, a frequencycorresponding to an energy difference between sublevels (Ms=0 and Ms=+1,−1) without Zeeman splitting is about 2.87 GHz, and therefore the coil 2applies a microwave of a predetermined frequency range including 2.87GHz (i.e. a frequency range that includes a range corresponding to ashift amount of the sublevels due to Zeeman splitting). The highfrequency power supply 12 causes the coil 2 to conduct a current of amicrowave (i.e. a current to generate the aforementioned microwave as amagnetic field).

The reference magnetic field generating unit 3 applies a referencemagnetic field (DC magnetic field) that causes Zeeman splitting of theenergy level of the plural specific color centers (here, plural NVcenters) in the ODMR member 1. A permanent magnet, a coil or the like isused as the reference magnetic field generating unit 3. If a coil isused as the reference magnetic field generating unit 3, a DC powersupply is installed and is electrically connected to this coil andsupplies DC current and thereby the reference magnetic field isgenerated. The aforementioned plural specific color centers haveorientations different from each other, and by the reference magneticfield, the energy level of the plural specific color centers isZeeman-splitted with different energy level shift amounts correspondingto the plural orientations, respectively.

The irradiating device 4 irradiates the ODMR member 1 with light(excitation light of a predetermined wavelength and measurement light ofa predetermined wavelength). The light receiving device 5 detectsfluorescence emitted from the ODMR member 1 when the ODMR member 1 isirradiated with the measurement light.

Further, the processor 11 includes a computer, for example, and executesa program with the computer and thereby acts as sorts of processingunits. In this embodiment, the processor 11 acts as a measurementcontrol unit 21 and a position estimating unit 22.

The measurement control unit 21 controls the high frequency power supply12 and the irradiating device 4 in accordance with a predetermined DCmagnetic field measurement sequence and thereby determines a detectionlight intensity of the fluorescence detected by the light receivingdevice 5 in the magnetic sensor unit 10. For example, the irradiatingdevice 4 includes a laser diode or the like as a light source, and thelight receiving device 5 includes a photo diode or the like as aphotodetector, and the measurement control unit 21 determines theaforementioned detection light intensity on the basis of an outputsignal of the light receiving device 5, and this output signal isobtained by amplification and/or the like of an output signal of thephotodetector.

In this embodiment, Ramsey Pulse Sequence is applied as theaforementioned predetermined DC magnetic field measurement sequence.However, the aforementioned DC magnetic field measurement sequence isnot limited to that.

The position estimating unit 22 estimates a position in 2 dimensions ofa surface of the test target object 100 and a position in a depthdirection of a magnetic field source that exists at an unspecifiedposition inside the test target object 100 on the basis of theintensities and the directions of the measurement target magnetic fielddetected by the magnetic sensor at at least two 2-dimensional positionsof the surface of the test target object 100.

FIG. 3 shows a perspective view that explains scanning of a magneticsensor 10 in Embodiment 1. The measurement control unit 21 controls adriving device such as a slider (not shown) and thereby scans themagnetic sensor unit 10 in a planar measurement area 111 in 2 dimensions(X direction and Y direction) of a surface of the test target object100, for example, as shown in FIG. 3, and performs magnetic fieldmeasurement using the magnetic sensor 10 at plural positions on thescanning path thereof. A pattern of the scanning path of the magneticsensor unit 10 is not limited to that shown in FIG. 3.

FIG. 4 shows a diagram that explain a magnetic field induced by acurrent as a magnetic field source. FIGS. 5A and 5B show diagrams thatexplains estimation of a position in a depth direction of a current as amagnetic field source in Embodiment 1.

As shown in FIG. 4, if a current I has substantially straight lineshape, the current I induces a rotational magnetic field in accordancewith Ampere's law. Therefore, an intensity and a direction of themagnetic field induced by the current I vary at positions in X direction(and/or Y direction on the scanning path.

Therefore, (a) a pair of two positions are detected such that (a1) aposition where the magnetic field intensity has a peak is locatedbetween the two positions on the scanning path and (a2) the magneticfield intensities measured at the two positions are substantiallyidentical to each other, (b) among the detected one or more pairs, apair is selected such that two vectors of a measured magnetic fields Bm1and Bm2 at the two positions lies on a single plane, and (c) as shown inFIG. 5A for example, with regard to the two positions (X1, Y1) and (X2,Y2) of the selected pair, derived is an intersection point of a normaldirection to a direction of the measured magnetic field Bm1 and a normaldirection to a direction of the measured magnetic field Bm2; and theposition of the current I corresponding to the measured magnetic fieldsBm1 and Bm2 is estimated as this intersection point.

It should be noted that if the single plane is tilted from a normaldirection of the surface of the test target object 100 by an angle ϕ,(i.e. the current I is tilted from a normal direction of the depthdirection), then the position in the depth direction of the current I iscorrected by cos (ϕ). Contrarily, if it is known that the current I isnot tilted from a normal direction of the depth direction (i.e. thecurrent I flows in parallel with the surface), then the determination ofthe angle ϕ and the correction by cos (ϕ) are not necessary because ϕ=90degrees.

Thus, in this case, the estimated position ZIest in the depth directionof the current I is derived in accordance with the following formula.ZIest=(D/2)*cos(θ)*cos(ϕ)−Zs

Here θ is an angle between a scanning surface (here the scanning plane)of the magnetic sensor unit 10 and the measured magnetic fields Bm1 andBm2. Further, Zs is a height from the surface of the test target object100 to the scanning surface of the magnetic sensor unit 10. Furthermore,D is a distance between the two positions (X1, Y1) and (X2, Y2).

In addition, estimated positions XIest and YIest of the current I in 2dimensional directions (X direction and Y direction) of the surface arederived from the two positions (X1, Y1) and (X2, Y2) and the measuredmagnetic fields Bm1 and Bm2 using a geometric computation as well.

Here the 3-dimensional position of the current I is estimated from themagnetic field measurement results at two positions. Alternatively, theposition of the current I may be estimated from the magnetic fieldmeasurement results at three or more positions (e.g. four positions).

Further, the position estimating unit 22 estimates a position in a depthdirection of the magnetic field source on the basis of (a) adistribution characteristic of the measurement target magnetic fieldcorresponding to a type (electric current in Embodiment 1) of themagnetic field source and (b) the intensities and the directions of themeasurement target magnetic field determined at the at least twopositions as mentioned.

If a type of the magnetic field source is a current of a substantiallystraight line shape, then a distribution characteristic of themeasurement target magnetic field is governed by Ampere's law asmentioned, and therefore a position in a depth direction of the magneticfield source is estimated on the basis of a known distributioncharacteristic induced by a current of a substantially straight lineshape. In such a manner, the position estimating unit 22 performscomputation corresponding to a type of the magnetic field source andthereby derives a position in a depth direction of the magnetic fieldsource from an intensity and a direction of the measurement targetmagnetic field.

If the type of the magnetic field source is unknown, then the positionestimating unit 22 may (a) estimate the type of the magnetic fieldsource from intensities and directions of the measurement targetmagnetic field obtained at plural positions on the scanning path and (b)estimate a position in a depth direction of the magnetic field source onthe basis of a distribution characteristic of the measurement targetmagnetic field corresponding to the estimated type of the magnetic fieldsource.

In this embodiment, the measurement control unit 21 controls the highfrequency power supply 12 and thereby changes a frequency of themicrowave, and determines a frequency characteristic of intensities ofthe light on the basis of the electronic signal obtained from the lightreceiving device 5 at each of predetermined plural positions (e.g. witha regular interval as an distance) on the aforementioned scanning path;and the position estimating unit 22 (a) determines a magnetic fieldcomponent due to the measurement target magnetic field corresponding toeach of the aforementioned plural orientations on the basis of thefrequency characteristic, (b) determines an intensity and a direction ofthe measurement target magnetic field on the basis of the magnetic fieldcomponents corresponding to the aforementioned plural orientations (i.e.by combining magnetic field component vectors corresponding to theplural orientations), and (c) estimates a position in a depth directionof the magnetic field source on the basis of the intensities and thedirections of the measurement target magnetic field determined at theaforementioned at least two positions.

FIG. 6 shows a diagram that explains plural orientations of an NVcenter. FIG. 7 shows a diagram that explains a frequency characteristicof fluorescence intensities (i.e. fluorescence intensity characteristicsto microwave frequency) corresponding to plural orientations of an NVcenter after Zeeman splitting of the NV center.

As shown in FIG. 6, in a diamond crystal, a nitrogen (N) adjacent to avacancy (V) can take four positions, and shift amounts of the sublevelsdue to Zeeman splitting are different from each other in these positions(i.e. orientations of a pair of the vacancy and the nitrogen),respectively. Therefore, as shown in FIG. 7, in a characteristic offluorescence intensities to frequencies of the microwave after Zeemansplitting due to the reference magnetic field, dip frequency pairs (fi+,fi−) corresponding to the orientations i appear differently from eachother.

Further, the direction of the measurement target magnetic field isdetermined by determining shift amounts dfi+ and dfi− of the four dipfrequency pairs (fi+, fi−) corresponding to the aforementioned fourorientations, respectively. Specifically, by an experiment or the like,a relationship was determined in advance between (a) an angle between areference direction in a geometric shape of the magnetic sensor unit 10and the direction of the measurement target magnetic field and (b) apattern of the shift amounts of the four dip frequency pairs (fi+, fi−);and the direction of the measurement target magnetic field is determinedfrom the shift amounts dfi+ and dfi− of the four dip frequency pairs(fi+, fi−) on the basis of the relationship. In addition, the intensityof the measurement target magnetic field is determined from magnitudesof the shift amounts of the four dip frequency pairs (fi+, fi−).

As mentioned, in this embodiment, the intensity and the direction of themeasurement target magnetic field is determined with the magnetic sensorunit 10 that uses diamond NV centers.

It should be noted that when other color centers are used as theaforementioned specific color centers instead of NV centers, theintensity and the direction of the measurement target magnetic field canbe determined in the same manner.

The current I inside the aforementioned test target object 100 may be aleakage current Ileak between electrodes inside the test target object100, for example. FIG. 8 shows a diagram that indicates an example of aleakage current as a magnetic field source that occurs betweenelectrodes inside a test target object. FIG. 9 shows a diagram thatindicates another example of a leakage current as a magnetic fieldsource that occurs between electrodes inside a test target object.

For example, as shown in FIG. 8, the aforementioned manner can estimatea position (i.e. leakage path) of a leakage current Ileak between twoelectrodes 121 that are perpendicular to the scanning plane (X-Y plane)of the magnetic sensor unit 10 and arrayed along a direction in parallelwith the scanning plane.

Further, for example, as shown in FIG. 9, the aforementioned manner canestimate a position (i.e. leakage path) of a leakage current Ileakbetween two electrodes 121 that are in parallel with the scanning plane(X-Y plane) of the magnetic sensor unit 10 and arrayed along a directionin parallel with the scanning plane.

The following part explains a behavior of the magnetic field sourcedetecting apparatus in Embodiment 1.

The measurement control unit 21 moves the magnetic sensor unit 10 alonga predetermined scanning pattern and causes the magnetic sensor unit 10to detect intensities and directions of a magnetic field atpredetermined measurement positions on the scanning path.

Subsequently, the position estimating unit 22 selects, as a measurementposition set, at least two measurement positions to be used for theposition estimation among all the measurement positions as mentioned,and estimates a position of a current I corresponding to the selectedmeasurement positions (i.e. a position in the depth direction (Zdirection) and a position on the surface (in X direction and Ydirection) corresponding to the position in the depth direction) on thebasis of the intensities and the directions of the magnetic fieldmeasured at the selected measurement positions as the measurementposition set.

In such a manner, the position estimating unit 22 extracts pluralmeasurement position set among all the measurement positions, estimatesa position of the current I corresponding to each of the measurementposition set, and consequently, determines a path of the current I.

As mentioned, in Embodiment 1, the magnetic sensor unit 10 detects anintensity and a direction of a measurement target magnetic field on orover the test target object 100. The position estimating unit 22estimates a position ZIest in a depth direction of a magnetic fieldsource (here, the current I) that exists at an unspecified positioninside the test target object 100 on the basis of the intensities andthe directions of the measurement target magnetic field detected by themagnetic sensor 10 at at least two 2-dimensional positions of thesurface of the test target object 100.

Consequently, a position of a magnetic field source in a depth directioninside the test target object 100 is estimated at a relatively low cost.

In particular, in Embodiment 1, a magnetic sensor that uses theaforementioned specific color centers is used in the magnetic sensorunit 10, and consequently, a position of a fine current such as leakagecurrent as a magnetic field source can be estimated.

Embodiment 2

Instead of moving the magnetic sensor unit 10, the magnetic field sourcedetecting apparatus in Embodiment 2 uses a sensor array in which theplural magnetic sensor units 10 are 2-dimensionally arrayed in themeasurement area 111, and an intensity and a direction of a magneticfield is measured at each position by the magnetic sensor unit 10fixedly arranged at this position. Subsequently, a position of amagnetic field source (electric current or the like) is estimated fromthe intensities and the directions of the magnetic field at thesepositions as well as in Embodiment 1.

Other parts of configuration and behaviors of the magnetic field sourcedetecting apparatus in Embodiment 2 are identical or similar to those inEmbodiment 1, and therefore not explained here.

Embodiment 3

In Embodiment 3, the magnetic field source is a magnetic object (i.e.ferromagnetism object) that has entered at an unspecified positioninside the nonmagnetic (i.e. paramagnetism) test target object 100, andthe magnetic field source detecting apparatus estimates a position ofthe magnetic object.

When the magnetic object is not magnetized, an external magnetic fieldis temporarily applied to the test target object and thereby themagnetic object is magnetized. Subsequently, if a shape of the magneticobject and/or a distribution characteristic of the measurement targetmagnetic field are/is known, then as well as in Embodiment 1 or 2, aposition (including a position in a depth direction) and an orientation(posture) of the magnetic object are estimated from a distribution ofintensities and directions of a magnetic field obtained at pluralposition in 2 dimension (i.e. X-Y plane).

Other parts of configuration and behaviors of the magnetic field sourcedetecting apparatus in Embodiment 3 are identical or similar to those inEmbodiment 1 or 2, and therefore not explained here.

It should be understood that various changes and modifications to theembodiments described herein will be apparent to those skilled in theart. Such changes and modifications may be made without departing fromthe spirit and scope of the present subject matter and withoutdiminishing its intended advantages. It is therefore intended that suchchanges and modifications be covered by the appended claims.

For example, in the aforementioned Embodiment 1 or 2, the aforementionedcurrent to be detected is a leakage current between electrodes asmentioned, for example. Alternatively, the aforementioned current to bedetected may be a current that flows on a wiring pattern or an internalleakage current in a semiconductor integrated circuit in a burn-in testof a semiconductor integrated circuit chip.

Further, in the aforementioned Embodiment 3, the aforementioned magneticobject to be detected is, for example, a metal piece that has entered infood as the test target material, a metal piece such as needle that hasentered in clothing as the test target material or the like.Furthermore, in the aforementioned Embodiment 3, the magnetic fieldsource detecting apparatus may be applied to a metal detector that isinstalled in an airport or the like, and the magnetic object to bedetected may be a metal product (e.g. knife, gun or the like) carried bya person as the test target object. Furthermore, in the aforementionedEmbodiment 3, the magnetic object to be detected may be a metalbiological tracer that is inserted to a living body of a person, ananimal, a plant or the like. If a shape of such a test target objectdoes not have a planar surface, then the test target object should bearranged under a (nonmagnetic) planer stage and the magnetic sensor unit10 should be scanned on or over the planer stage.

Furthermore, in the aforementioned Embodiment 3, the external magneticfield to magnetize the magnetic object to be detected and theaforementioned reference magnetic field may be generated by a singlemagnetic field generating unit.

Furthermore, in Embodiment 1, 2 or 3, the ODMR member 1 includes diamondNV centers as the aforementioned specific color centers. Alternatively,SiV centers, GeV centers, SnV centers or the like may be used in theODMR member 1. In addition, a crystal as a base material that includesthe specific color centers may be SiC other than diamond.

Furthermore, in Embodiment 1, 2 or 3, an intensity and a direction of anenvironmental magnetic field such as geomagnetism may be measured usinganother magnetic sensor unit identical or similar to the magnetic sensorunit 10 at a position that is not affected by the measurement targetmagnetic field, and an intensity and a direction of the measurementtarget magnetic field obtained by the magnetic sensor unit 10 may becorrected with the measured intensity and direction of the environmentalmagnetic field.

Furthermore, in Embodiment 1, 2 or 3, analysis of the magnetic fielddistribution ϕ (x, y, z) in the test target object may be performedusing formulas shown in FIG. 10 on the basis of intensities ϕm of themeasurement target magnetic field obtained by the magnetic sensor unit10 on the measurement surface (i.e. the scanning plane), and a positionof the magnetic field source may be estimated from the magnetic fielddistribution ϕ (x, y, z). Specifically, in a steady magnetic field, amagnetic field intensity ϕ, in a Z direction satisfies Laplace'sequation as shown in Formula (1). When Fourier transformation isperformed for the magnetic field intensity ϕ as shown in Formula (2) andinverse Fourier transform is performed for the magnetic field intensityafter Fourier-transformation, Formula (3) is obtained.Fourier-transformation of the magnetic field intensity ϕm obtained onthe measurement surface and differentiation of it by Z are defined asshown in Formula (4), the magnetic field intensity afterFourier-transformation is obtained through Fourier-transformation fromthe magnetic field intensity ϕm as shown in Formula (5), and the targetmagnetic field distribution ϕ (x, y, z) is obtained as shown in Formula(6) by inverse Fourier transform of the magnetic field intensity afterFourier transform shown in Formula (5).

INDUSTRIAL APPLICABILITY

For example, the present invention is applicable to detection of amagnetic field source.

What is claimed is:
 1. A magnetic field source detecting apparatus,comprising: a magnetic sensor unit, comprising an optically detectedmagnetic resonance member, that detects an intensity and a direction ofa measurement target magnetic field on or over a surface of a testtarget object; and a position estimating unit that estimates a positionin a depth direction of a magnetic field source that exists at anunspecified position inside the test target object on the basis of theintensities and the directions of the measurement target magnetic fielddetected by the magnetic sensor at at least two 2-dimensional positionsof the surface.
 2. A magnetic field source detecting apparatus,comprising: a magnetic sensor unit that detects an intensity and adirection of a measurement target magnetic field on or over a surface ofa test target object; a position estimating unit that estimates aposition in a depth direction of a magnetic field source that exists atan unspecified position inside the test target object on the basis ofthe intensities and the directions of the measurement target magneticfield detected by the magnetic sensor at at least two 2-dimensionalpositions of the surface; a measurement control unit; and a referencemagnetic field generating unit; wherein the magnetic sensor unitcomprises an optically detected magnetic resonance member, a coil thatapplies a magnetic field of a microwave to the optically detectedmagnetic resonance member, an irradiating device that irradiates theoptically detected magnetic resonance member with light, and a lightreceiving device that detects light that the optically detected magneticresonance member emits and outputs an electronic signal corresponding tothe detected light; the optically detected magnetic resonance membercomprises plural specific color centers; the specific color center has aZeeman-splittable energy level and can take plural orientations of whichenergy level shift amounts due to Zeeman splitting are different fromeach other; the reference magnetic field generating unit applies areference magnetic field that causes Zeeman splitting of the energylevel of the plural specific color centers; the plural specific colorcenters have plural orientations different from each other, and theenergy level of the plural specific color centers is Zeeman-splittedwith different energy level shift amounts corresponding to the pluralorientations by the reference magnetic field, respectively; themeasurement control unit changes a frequency of the microwave anddetermines a frequency characteristic of intensities of the light on thebasis of the electronic signal at each of predetermined pluralpositions; and the position estimating unit (a) determines a magneticfield component due to the measurement target magnetic fieldcorresponding to each of the plural orientations on the basis of thefrequency characteristic, (b) determines an intensity and a direction ofthe measurement target magnetic field on the basis of the magnetic fieldcomponents corresponding to the plural orientations, and (c) estimates aposition in a depth direction of the magnetic field source on the basisof the intensities and the directions of the measurement target magneticfield determined at the at least two positions.
 3. The magnetic fieldsource detecting apparatus according to claim 1, wherein the positionestimating unit estimates a position in a depth direction of themagnetic field source on the basis of (a) a distribution characteristicof the measurement target magnetic field corresponding to a type of themagnetic field source and (b) the intensities and the directions of themeasurement target magnetic field determined at the at least twopositions.
 4. The magnetic field source detecting apparatus according toclaim 1, wherein the test target object is composed of a nonmagneticmaterial and the magnetic field source is (a) a current that flows at anunspecified position inside the test target object or at one ofconduction paths laid in multilayers or (b) a magnetic object that hasentered at an unspecified position inside the test target object.
 5. Amagnetic field source detecting method comprising the steps of:detecting intensities and directions of a measurement target magneticfield at at least two 2-dimensional positions of a surface of a testtarget object using a magnetic sensor unit, comprising an opticallydetected magnetic resonance member, that detects an intensity and adirection of the measurement target magnetic field on or over thesurface of the test target object; and estimating a position in a depthdirection of a magnetic field source that exists at an unspecifiedposition inside the test target object on the basis of the intensitiesand the directions of the measurement target magnetic field detected atthe at least two 2-dimensional positions.
 6. The magnetic field sourcedetecting apparatus according to claim 1, wherein the magnetic sensorunit is controlled to move along a predetermined scanning path.
 7. Themagnetic field source detecting apparatus according to claim 1, whereinthe magnetic field source detecting apparatus comprises a sensor arrayin which a plural of the magnetic sensor units are arrayed in ameasurement area.
 8. The magnetic field source detecting apparatusaccording to claim 1, wherein the magnetic sensor unit further comprisesa coil that applies a magnetic field of a microwave to the opticallydetected magnetic resonance member, an irradiating device thatirradiates the optically detected magnetic resonance member with light,and a light receiving device that detects light that the opticallydetected magnetic resonance member emits and outputs an electronicsignal corresponding to the detected light.
 9. The magnetic field sourcedetecting apparatus according to claim 1, wherein the positionestimating unit determines the intensity and the direction of themeasurement target magnetic field on the basis of magnetic fieldcomponents corresponding to plural orientations, and estimates aposition in a depth direction of the magnetic field source on the basisof the intensities and the directions of the measurement target magneticfield determined at least two positions.
 10. The magnetic field sourcedetecting apparatus according to claim 1, wherein the optically detectedmagnetic resonance member comprises plural specific color centers.